Drive track and drive sprocket for a vehicle

ABSTRACT

A drive track for a tracked vehicle has an endless belt having an inner surface and an outer surface. The belt defines a longitudinal direction and a lateral direction. A plurality of external lugs project outwards from the outer surface of the belt. Each of the plurality of external lugs has a height in a direction normal to the outer surface. The plurality of external lugs forms a plurality of lateral rows. A longitudinal spacing between consecutive lateral rows of the plurality of lateral row is an external lug pitch. The height of at least some of the plurality of external lugs is greater than the external lug pitch. Drive sprocket and drive track assemblies and vehicles having the drive track are also presented.

CROSS-REFERENCE

The present application is a continuation of International PatentApplication No. PCT/IB2014/060283 filed on Mar. 28, 2014 which claimspriority to U.S. Provisional Patent Application No. 61/806,363 filed onMar. 28, 2013, the entirety of both of which is incorporated herein byreference.

FIELD OF THE TECHNOLOGY

The present technology relates to endless drive tracks and drivesprockets for vehicles.

BACKGROUND

Vehicles such as snowmobiles are provided with endless drive tracks toenable traveling over surfaces such as snow, ice and mud. The endlessdrive tracks are driven by the vehicle's engine via one or moresprockets which engage the endless drive tracks to move the drive tracksand thereby propel the vehicle. Traction between the drive tracks andthe ground enables the snowmobile to travel on soft-snow coveredsurfaces.

Although current drive tracks provide adequate traction, it would bedesirable to have an endless drive track for a vehicle that can providegreater traction in soft surfaces such as snow.

SUMMARY

In one aspect, the present provides a drive track for a tracked vehicle.The drive track has an endless belt having an inner surface and an outersurface. The belt defines a longitudinal direction and a lateraldirection. A plurality of external lugs project outwards from the outersurface of the belt. Each of the plurality of external lugs has a heightin a direction normal to the outer surface. The plurality of externallugs forms a plurality of lateral rows. A longitudinal spacing betweenconsecutive lateral rows of the plurality of lateral row is an externallug pitch. The height of at least some of the plurality of external lugsis greater than the external lug pitch.

In another aspect, the height of all of the external lugs of at leastsome of the lateral rows is greater than the external lug pitch.

In yet another aspect, the height of all of the plurality of externallugs is greater than the external lug pitch.

In a further aspect, the adjacent lateral rows have different numbers.

In another aspect, the alternating lateral rows have equal numbers ofexternal lugs.

In an additional aspect, the external lug pitch is 7.62 cm (3 inches).

In another aspect, the drive track of also includes a plurality ofinternal lugs projecting inwards from the inner surface of the belt. Theplurality of internal lugs format least one longitudinal row. Alongitudinal spacing between consecutive internal lugs of the at leastone longitudinal row is an internal lug pitch.

In another aspect, a snowmobile includes a frame, a suspension assemblyand an engine connected to the frame, and a drive axle operativelyconnected to the engine. At least one drive sprocket mounted on thedrive axle is rotatable therewith. Each of the at least one drivesprocket includes a wheel mounted on the drive axle and a plurality ofteeth being distributed on a periphery of the wheel. A circumferentialspacing between consecutive teeth of the plurality of teeth is asprocket pitch. A drive track is connected to the frame by thesuspension assembly. The drive sprocket drives the drive track about thesuspension assembly to propel the snowmobile. The drive track includesan endless belt having an inner surface and an outer surface. The beltdefines a longitudinal direction and a lateral direction. A plurality ofexternal lugs project outwards from the outer surface of the belt. Eachof the plurality of external lugs has a height in a direction normal tothe outer surface. The plurality of external lugs forms a plurality oflateral rows. A longitudinal spacing between consecutive lateral rows ofthe plurality of lateral row is an external lug pitch. The height of atleast some of the plurality of external lugs is greater than theexternal lug pitch.

In a further aspect, a plurality of internal lugs project inwards fromthe inner surface of the belt. Each of the plurality of teeth is adaptedto selectively engage at least some of the plurality of internal lugs.The plurality of internal lugs forms at least one longitudinal row. Alongitudinal spacing between consecutive internal lugs of the at leastone longitudinal row is an internal lug pitch. The internal lug pitch iscomplementary to the sprocket pitch of the at least one drive sprocketsuch that two consecutive sprocket teeth of the plurality of sprocketteeth of the at least one drive sprocket contact one of the internallugs.

In another aspect, the wheel of the drive sprocket has a diameter suchthat the plurality of teeth engages at least three of the plurality ofinternal lugs.

In an additional aspect, the plurality of teeth includes a plurality ofaxial teeth being distributed on a periphery of an axial surface of thewheel and extending therefrom in an axial direction of the drive axle.

In an additional aspect, the plurality of teeth of includes a pluralityof radial teeth distributed on a perimetrical surface of the wheel andextending radially therefrom. The drive track includes a plurality ofbelt apertures extending through the belt from the inner surface to theouter surface. The belt apertures form at least one longitudinal row ofbelt apertures. The longitudinal spacing between consecutive beltapertures of the at least one longitudinal row of belt apertures is abelt aperture pitch. The belt aperture pitch corresponds to the sprocketpitch of the radial teeth such that each of the plurality of radialteeth selectively engages a corresponding belt aperture when a surfaceof the wheel adjacent to the corresponding radial tooth is in contactwith the inner surface adjacent the corresponding belt aperture.

In another aspect, the external lug pitch is 7.62 cm (3 inches).

In another aspect, the plurality of axial teeth is at least seven axialteeth.

In yet another aspect, the plurality of axial teeth is seven axialteeth.

In a further aspect, a brake disk is mounted on the drive axle. Thebrake disk is coaxial and rotatable with the drive axle. A diameter ofthe brake disk is greater than a diameter of the wheel of the at leastone drive sprocket.

In an additional aspect, the diameter of the brake disk is greater thana diameter of a cylinder circumscribing the entirety of the at least onedrive sprocket.

In a further aspect, the frame has a tunnel, the tunnel having a leftside wall defining a left opening and a right side wall defining a rightopening. A left end of the drive axle extends through the left openingand a right end of the drive axle extends through the right opening. Thedrive axle and the at least one drive sprocket mounted thereon arerotatable about a drive sprocket axis. The snowmobile further includes aleft footrest extending laterally outwardly from the left side wall. Aportion of the left footrest is disposed longitudinally forwardly of thedrive sprocket axis. A projection of the left footrest on the left sidewall is disposed in part within the left opening. A right footrestextends laterally outwardly from the right side wall. A portion of theright footrest is disposed longitudinally forwardly of the drivesprocket axis. A projection of the right footrest on the right side wallis disposed in part within the right opening.

In yet another aspect, the suspension assembly is a rear suspensionassembly. The rear suspension assembly includes an upper idler wheelrotatable about an upper idler wheel rotation axis. The drive axle andthe at least one drive sprocket mounted thereon are rotatable about adrive sprocket axis. The snowmobile further includes a left ski assemblyand a right ski assembly. A left front suspension assembly connects theleft ski assembly to the frame. A right front suspension assemblyconnects the right ski assembly to the frame. Each of the left and rightfront suspension assemblies includes an arm having a front member and arear member, respective inner ends of each of the front and rear membersbeing pivotally connected to the frame about an arm pivot axis. For eachof the left and right suspension assemblies, an intersection of the armpivot axis with a plane containing the upper idler wheel rotation axisand the drive sprocket axis is disposed longitudinally between the innerends of the front member and the rear member.

In a further aspect, the arm is a lower arm and each of the left andright front suspension assemblies further includes an upper arm.

In another aspect, a drive sprocket and drive track assembly of atracked vehicle includes a drive track having an endless belt. Theendless belt has an inner surface and an outer surface. The belt definesa longitudinal direction and a lateral direction. A plurality ofexternal lugs project outwards from the outer surface of the belt. Eachof the plurality of external lugs has a height in a direction normal tothe outer surface. The plurality of external lugs forms a plurality oflateral rows. A longitudinal spacing between consecutive lateral rows ofthe plurality of lateral row is an external lug pitch. The height of atleast some of the plurality of external lugs is greater than theexternal lug pitch. A plurality of internal lugs project inwards fromthe inner surface of the belt. The plurality of internal lugs forms atleast one longitudinal row. A longitudinal spacing between consecutiveinternal lugs of the at least one longitudinal row is an internal lugpitch. At least one drive sprocket is included. Each of the at least onedrive sprocket includes a wheel mounted on the drive axle and aplurality of teeth distributed on a periphery of the wheel. Acircumferential spacing between consecutive teeth of the plurality ofteeth is a sprocket pitch. Each of the plurality of teeth is adapted toengage at least some of the plurality of internal lugs. The internal lugpitch is complementary to the sprocket pitch of the at least one drivesprocket such that two consecutive teeth of the plurality of teeth ofthe at least one drive sprocket contact one of the internal lugs.

In a further aspect, the sprocket has a diameter such that the pluralityof teeth engages at least three of the plurality of internal lugs.

For purposes of the present application, terms related to spatialorientation when referring to a snowmobile and components in relation tothe snowmobile, such as “forwardly”, “rearwardly”, “left”, “right”,“above” and “below”, are as they would be understood by a driver of thesnowmobile, with the snowmobile in a straight ahead orientation (i.e.not steered left or right), and in an upright position (i.e. nottilted). When referring to a drive track of the snowmobile alone, termsrelated to spatial orientation, such as “lateral” and “longitudinal”should be taken with respect to the drive track itself.

Embodiments of the present technology each have at least one of theabove-mentioned aspects, but do not necessarily have all of them.

Additional and/or alternative features, aspects, and advantages ofembodiments of the present technology will become apparent from thefollowing description, the accompanying drawings, and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present technology, as well as otheraspects and further features thereof, reference is made to the followingdescription which is to be used in conjunction with the accompanyingdrawings, where:

FIG. 1 is a right side elevation view of a snowmobile;

FIG. 2 is a left side elevation view of a portion of the snowmobile ofFIG. 1 showing a portion of a frame of the snowmobile, with a drivetrack connected to the frame by a rear suspension assembly;

FIG. 3 is a top plan view of the portion of the snowmobile of FIG. 1;

FIG. 4 is a vertical cross-sectional view taken along the line A-A ofFIG. 2; and

FIG. 5 is a perspective view, taken from a top, rear and left side, of aportion of the snowmobile of FIG. 1 showing a portion of the drive trackof FIG. 3 being engaged by a pair of sprockets mounted on a drive axleconnected to a reduction drive;

FIG. 6A is a left side elevation view of the snowmobile portion of FIG.5 with a drive track having a first embodiment of external lugs;

FIG. 6B is a left side elevation view of the snowmobile portion of FIG.5 with a drive track having a second embodiment of external lugs;

FIG. 7 is a top plan view of the snowmobile portion of FIG. 5;

FIG. 8 is a cross-sectional view of the snowmobile portion of FIG. 5taken along the line B-B of FIG. 7;

FIG. 9 is a perspective view taken from a top, right and rear side, ofthe snowmobile portion of FIG. 5 showing a brake disc mounted on thedrive axle with the reduction gear removed for clarity;

FIG. 10 is a right side elevation view of the snowmobile portion of FIG.9 with the track removed for clarity;

FIG. 11A is a perspective view taken from a front, right side of aportion of a drive track according to another embodiment;

FIG. 11B is another perspective view taken from a front, right side ofthe portion of the drive track of FIG. 11A;

FIG. 12A is a top plan view of a portion of a drive track according toyet another embodiment;

FIG. 12B is a right side elevation view of the portion of the drivetrack of FIG. 12A;

FIG. 12C is a cross-sectional view of the portion of the drive track ofFIG. 12A taken along the line C-C of FIG. 12A;

FIG. 13 is a top plan view of a tunnel of the snowmobile of FIG. 1having an embodiment of a heat exchanger assembly;

FIG. 14 is a bottom plan view of the tunnel and heat exchanger assemblyof FIG. 13;

FIG. 15A is a cross-sectional view taken along the line 15A-15A of FIG.13;

FIG. 15B is a cross-sectional view taken along the line 15B-15B of FIG.14;

FIG. 15C is a cross-sectional view taken along the line 15C-15C of FIG.14; and

FIG. 15D is a cross-sectional view taken along the line 15D-15D of FIG.14;

FIG. 16 is a left side elevation view of a portion of a frame and alower A-arm of the front suspension assembly of the snowmobile of FIG.1;

FIG. 17A is a cross-sectional view taken along the line 17-17 of FIG.16;

FIG. 17B is a cross-sectional view taken along the line 17-17 of FIG. 16and including the front drive axle and the drive sprockets of thesnowmobile of FIG. 1.

DETAILED DESCRIPTION

With reference to FIG. 1, a snowmobile 10 will be described. Although asnowmobile 10 is presented herein, it is contemplated that aspects ofthe present technology could be applied to other types of vehicleshaving drive tracks for operation on snow or other surfaces.

The snowmobile 10 includes a front end 12 and a rear end 14, which aredefined consistently with the forward travel direction of the snowmobile10.

The snowmobile 10 includes a frame 16. The frame 16 includes a tunnel18, an engine cradle portion 20, a left front suspension assemblymounting portion and a right front suspension assembly mounting portion22. An engine 24 (schematically shown) is supported by the engine cradleportion 20. The engine 24 is cooled by coolant circulated through a heatexchanger assembly 300, 400 (FIG. 3, 13), described in greater detailbelow. The heat exchanger assembly 300, 400 forms part of the tunnel 18.

An endless drive track 30 is positioned under the tunnel 18. The endlessdrive track 30 is operatively connected to the engine 24 through a belttransmission system 26 (schematically shown) for propelling thesnowmobile over the ground. The transmission system 26 is a continuouslyvariable transmission (CVT) but it is contemplated that other types oftransmissions could be used. The CVT 26 is disposed on a left side ofthe engine 24.

The endless drive track 30 is suspended for movement relative to theframe 16, by a rear suspension assembly 32. The rear suspension assembly32 includes a pair of spaced apart slide rails 34, rear suspension arms36, 38 and shock absorbers 40, 42. The slide rails 34 engage the innersurface 220 a (FIG. 5) of the endless drive track 30, the rearsuspension arms 36, 38 and the shock absorbers 40, 42 pivotally connectbetween the tunnel 18 and the slide rails 34. The endless drive track 30is driven to run about the rear suspension assembly 32 for propulsion ofthe snowmobile 10. The rear suspension assembly 32 includes a pluralityof idler wheels 44 rotatably supported by the frame 16 which define thepath over which the endless drive track 30 travels. The tunnel 18defines a longitudinal direction 3 (FIG. 3) and a lateral direction 4(FIG. 3) for the snowmobile 10. A longitudinal centerplane 13 of thesnowmobile 10 extends vertically and longitudinally.

A seat 48, disposed on the tunnel 18, supports a rider. A footrest 50 ispositioned on each side of the tunnel 18 below the seat 48 to supportthe rider's feet. The footrests 50 are integrally formed with the tunnel18. As can be seen best in FIGS. 13 and 16, the left footrest 50 has aportion 50 a extending generally horizontally and laterally outwardlyfrom the left side wall 18 b of the tunnel 18. A rim 50 b extendsvertically upwards from the laterally outer edge of the horizontalportion 50 a. The upper surface of the rim 50 b has a number of spikes50 c projecting upwards therefrom. A vertically and laterally extendingwall forms a toehold 51 at the front end of the footrest 50. The toehold51 extends upwards from the horizontal footrest portion 50 a andlaterally outwards from the side wall 18 b of the tunnel 18. Similarly,the right footrest 50 has a horizontal portion 50 a, a vertical rim 50 bformed at the laterally outer edge of the horizontal portion 50 a,spikes 50 c projecting upwards from the upper rim surface, and a toehold51 extending laterally and vertically from the front end of thehorizontal portion 50 a. The spikes 50 c provide a better grip on thefootrest 50 for the driver's foot and help prevent the foot from slidinglaterally off the footrest 50. The toehold 51 helps prevent the driver'sfoot from sliding off the front edge of the footrest 50.

Left and right ski assemblies 52 are positioned at the front end 12 ofthe snowmobile 10. Each ski assembly 52 includes a ski 54 and acorresponding ski leg 56. Each of the left and right ski assemblies 52is attached to the respective front suspension assembly mounting portion22 of the frame 16 via a respective front suspension assembly 28. Theleft front suspension assembly 28 is a mirror image of the right frontsuspension assembly 28, and therefore, only the left front suspensionassembly 28 will be described herein. The left front suspension assembly28 includes an upper A-arm 28 a (FIG. 1) and a lower A-arm 28 b (FIG.16). Each A-arm 28 a, 28 b has a front member and a rear member that areconnected together at their laterally outer ends and longitudinallyspaced apart at their laterally inner ends. The outer ends of the frontand rear members of the upper A-arm 28 a are connected to an upperportion of the left ski leg 56 via a ball joint (not shown). The outerends of the front and rear members of the lower A-arm 28 b are connectedto a lower portion of the left ski leg 56 via a ball joint (not shown).The laterally inner ends of the upper A-arm 28 a are rotatably connectedto the left front suspension assembly mounting portion 22 so as to pivotabout a longitudinally extending pivot axis. The laterally inner ends ofthe lower A-arm 28 b are rotatably connected to the left frontsuspension assembly mounting portion 22 to pivot about a longitudinallyextending pivot axis 29 b. It is contemplated that other types of frontsuspension assemblies could be used. It is contemplated that thesnowmobile 10 could have only one ski 56 and one ski leg 54.

A steering assembly 60 including a steering column 62 and handlebar 64is provided. The steering column 62 is attached at its upper end to thehandlebar 64, which is positioned forward of the rider and behind theengine 24. The steering column 62 is operatively connected to the skilegs 56 and the skis 54, in order to steer the skis 54, and thesnowmobile 10, when the handlebar 64 is turned. It is contemplated thatthe steering column 62 could be connected to a steering device otherthan the handlebar 64.

Fairings 66 are provided at the front end 12 of the snowmobile 10. Thefairings 66 enclose the engine 24 and the belt transmission system 26,thereby providing an external shell that not only protects the engine 24and the belt transmission system 26, but also make the snowmobile 10more aesthetically pleasing. The fairings 66 include a hood and one ormore side panels that can be opened to allow access to the engine 24 andthe belt transmission system 26 when this is required, for inspection ormaintenance of the engine 24 and/or the belt transmission system 26 forexample. A windshield 68 is connected to the fairings 66 near the frontend 12 of the snowmobile 10. It is contemplated that the windshield 68could be attached directly to the handlebar 64. The windshield 68 actsas a windscreen to lessen the force of the air on the rider while thesnowmobile 10 is moving forward. A snow flap 69 is connected to thetunnel 18 at the rear end 14 of the snowmobile 10 to protect from snowand ice being flung upwards as the snowmobile 10 travels over the ground2.

With reference to FIGS. 2 to 4, the endless track 30 is operativelyconnected to the engine 24 via a drive axle 70 and a fixed ratioreduction drive 74. The CVT 26 is disposed on a left side of the engine24. The reduction drive 74, disposed on a right side of the engine 24and the tunnel 18, is connected to the CVT 26 by a transverse jackshaft72. A driven pulley (not shown) of the CVT 26 is mounted on the left endof the transverse jackshaft 72. An input member of the reduction drive74 is mounted on the right end of the jackshaft 72. The output member ofthe reduction drive 74 is mounted on the right end of the drive axle 70.The drive axle 70 is thus rotated by the engine 24.

With reference to FIGS. 4 and 5, two drive sprockets 80, including aleft drive sprocket 80 and a right drive sprocket 80, are mountedcoaxially to the drive axle 70 to be rotated thereby. The drivesprockets 80 and the drive axle 70 rotate about a drive sprocket axis85. It is contemplated that only one or more than two drive sprockets 80could be mounted on the drive axle 70. The engine 24 thereby drives thesprockets 80 and the track 30 to propel the snowmobile 10.

With reference to FIGS. 2, 9 and 10, the left end of the drive axle 70has a brake disc 76 coaxially mounted thereon. The brake disc 76 rotateswith the drive axle 70 about the axis 85. The brake disc 76 isselectively engaged by a brake caliper (not shown) connected to a brakeactuator (not shown) mounted on the handlebar 64. Upon actuation of thebrake actuator, the brake caliper applies a force on the brake disk 76,in a direction opposite to the torque applied by the engine 24 in orderto slow down or stop motion of the snowmobile 10.

With reference to FIGS. 2 to 5, the elongated tunnel 18 has a left sidewall 18 b, a top wall 18 a and a right side wall 18 b forming aninverted U-shaped structure when viewed from the front. A longitudinallyextending gap 18 c is defined in the top wall 18 a. The gap 18 c extendsalong the longitudinal centerplane 13. Each side wall 18 b has an upperfront edge 18 d that extends downwards and forwards from the front endof the top wall 18 a, and a lower front edge 18 e that extends downwardsand forwards from the upper front edge 18 d. The upper and lower frontedges 18 d, 18 e of the left and right side walls 18 b form the front ofthe tunnel 18.

The drive axle 70 extends laterally through the forward portion of thetunnel 18 such that the left end of the drive axle 70 extends out of aleft circular opening 19 defined in the left side wall 18 b of thetunnel 18 and the right end of the drive axle 70 extends out of a rightcircular opening 19 defined in the right side wall 18 b of the tunnel18. The sprockets 80 are disposed inside the tunnel 18 between the leftand right side walls 18 b as can be seen in FIG. 4. The brake disk 76 ismounted on the left end of the drive axle 70 outside the tunnel 18adjacent to the left side wall 18 b as can be seen in FIG. 2. The driveaxle 70 is disposed rearward of the engine cradle portion 20. The enginecradle portion 20 is disposed lower than the drive axle 70 and thesprockets 80. The vertical position of the drive axle 70 and thesprockets 80 mounted thereon is determined such that the drive axle 70and the sprockets 80 are sufficiently spaced from the ground to avoidinterference with obstructions such as rocks, etc. such that a center ofgravity of the snowmobile 10 is sufficiently low to provide goodhandling.

As can be seen in FIG. 16, the front edge of the opening 19 is disposedlongitudinally rearward of the toehold 51. A plane 81 containing thedrive sprocket axis 85 and a rotation axis 44 a of the upper idler wheel44 intersects the pivot axis 29 b of each of the left and right lowerfront suspension A-arms 28 b. The pivot axis 29 b intersects the plane81 at a location that is longitudinally between the front and rearmembers of the lower front suspension A-arm 28 b.

With reference to FIGS. 17A and 17B, the rim 50 b of the footrest 50 andthe spikes 50 c extending upwards therefrom extend vertically higherthan the lower edge of the left opening 19. As can be seen best in FIG.17B, a horizontal plane 356 passing through the top of the spikes 50 cis disposed above a horizontal plane 19 a (FIG. 17B) passing through thebottom of the opening 19. As can be seen in FIG. 17A, the lower surfaceof the drive axle 70 is also disposed vertically below the plane 356passing though the top of the spikes 50 c.

With reference to FIGS. 5 to 10, each sprocket 80 includes three sets ofsprocket teeth 90, 100, 110 by which the sprocket 80 engages the track30. The teeth 90, 110 are axial teeth that engage corresponding internallugs (or track lugs, or track teeth) 260 of the endless drive track 30to provide traction between the sprockets 80 and the endless drive track30. The teeth 100 are radial teeth 100 that engage apertures 240 of thedrive track 30 between the internal lugs 260. While two sprockets 80 areused in the illustrated embodiments, it is contemplated that the numberof sprockets 80 could be one or greater than two.

The two drive sprockets 80 (left and right) being identical, only a leftdrive sprocket 80 will be described. The drive sprocket 80 comprises agenerally disc-shaped sprocket wheel 150 that has an outer perimetricalsurface 160 and two opposing axial surfaces 170, 180. The sprocket wheel150 has a central bore 190 through which the drive axle 70 extends. Thebore 190 and the drive axle 70 have mating cross-sections thatrotationally secure the sprocket 80 to the drive axle 70. Alternativemethods of rotationally securing the sprocket 80 to the drive axle 70may also be used (e.g., a key and keyway, square cross-sections, radialpins, etc.).

As best seen in FIG. 10, the sprocket wheel 150 has a diameter 82. Thesprocket 80 has a diameter 84 as defined by a diameter of a cylinder 87circumscribing the entirety of the sprocket 80 including the radialteeth 100. The diameter 84 of the sprocket 80 is smaller than thediameter 77 of the brake disc 76 mounted on the drive axle 70 laterallyoutward of the sprocket 80.

The axial sprocket teeth 90 are circumferentially-spaced teeth thatproject axially outwardly from the axial surface 180, and the sprocketteeth 110 comprise circumferentially-spaced teeth that project axiallyoutwardly from the axial surface 170. It is contemplated that the axialsprocket teeth 90, 110 could be mirror images of each other. The outeraxial surface 180 curves axially inwards between consecutive outer axialsprocket teeth 90. The inner axial surface 170 is substantially planarbetween consecutive inner axial sprocket teeth 110. The radial sprocketteeth 100 comprise circumferentially-spaced teeth that project radiallyoutwardly from the wheel 150. The perimetrical surface 160 forms asprocket valley 200 between consecutive sprocket teeth 100.

The drive sprocket 80 has seven sprocket teeth 90, seven sprocket teeth100, and seven sprocket teeth 110. It is contemplated that the drivesprocket 80 could have more or less than seven sprocket teeth 90, sevensprocket teeth 100, and seven sprocket teeth 110.

The sprocket teeth 90, 100, 110 are aligned with each other in thecircumferential direction such that each axial sprocket tooth 90 isdisposed at the same circumferential position as a corresponding one ofthe axial sprocket teeth 110 and a corresponding one of the radialsprocket teeth 100. It is contemplated that the sets of sprocket teeth90, 100, 110 could be offset from one another in the circumferentialdirection.

As best seen in FIG. 5, each axial tooth 90 has a radially outer surface92 and an axially outer surface 94. Each axial tooth 110 has a radiallyouter surface 112 and an axially outer surface 114. The axially outersurfaces 92, 112 are curved axially inwards in the middle portionthereof. Each axial tooth 90 is formed integrally with the correspondingaxial tooth 110. The radially outer surfaces 92 and 112 form acontinuous surface extending across the perimetrical surface 160 of thewheel 150 and disposed radially outwards of the perimetrical surface160.

The corresponding radial tooth 100 extends radially outwards from thecontinuous surface 92, 112. Each radial tooth 100 is formed integrallywith the corresponding axial teeth 90, 110. It is contemplated that thecorresponding teeth 90, 100, 110 could not be formed integrally.

With reference to FIGS. 8 and 10, consecutive axial sprocket teeth 90are disposed at an angular sprocket pitch 88 from each other.Consecutive axial sprocket teeth 110 are also disposed at the angularsprocket pitch 88 from each other. Furthermore, consecutive radialsprocket teeth 100 are also disposed at the angular sprocket pitch 88from each other. The angular sprocket pitch 88 is 51.4 degrees. It iscontemplated that the sprocket pitch 88 could be more or less than 51.4degrees depending on the number of sprocket teeth 90, 100, 110. Forexample the sprocket pitch 88 could be 40 degrees if the sprocket 80 hadnine teeth 90. It is contemplated that the axial sprocket teeth 90, 110could have a sprocket pitch different from a sprocket pitch of theradial sprocket teeth 100. It is also contemplated that the axialsprocket teeth 90 could have a sprocket pitch different from a sprocketpitch of the axial sprocket teeth 100.

As the drive track 30 moves over the sprocket 80, the surfaces 92, 112of the axial teeth 90, 110 contact the inner surface 220 a of the drivetrack 30. The circumferential spacing between consecutive teeth 90, 110can be described as a circumferential sprocket pitch 86 for the sprocket80. With reference to FIG. 10, a circumferential sprocket pitch 86 forthe sprocket 80 can be defined based on the circumferential spacingalong a cylinder 83 circumscribing the radially outer surfaces 92, 112.The circumferential sprocket pitch 86 for the sprocket 80 would be givenby the spacing 86 on the cylinder 83 between the centers of consecutiveteeth 90 or 100 or 110.

A circumferential sprocket pitch could similarly be defined for aparticular set of teeth 90, 100, 110 of the sprocket 80 by thecircumferential spacing along a cylinder circumscribing that particularset of teeth. For example, the circumferential axial teeth pitch for theaxial teeth 90, 110 would be the circumferential sprocket pitch 86measured along the cylinder 83. The circumferential radial teeth pitchfor the radial teeth 100 would be the spacing 89 along the cylinder 87.

The sprocket pitches 86, 88 are determined based on a pitch 266(discussed further below) between consecutive internal lugs 120 in orderto ensure traction between the sprocket 80 and the drive track 30.

The sprocket wheel 150 and the sprocket teeth 90, 100, 110 areintegrally formed as mentioned above. To reduce the weight of thesnowmobile 10, the sprocket 80 is made of a strong, light material (suchas plastic). It is contemplated that the sprocket 80 could be made ofany other material including steel or a composite material includingaluminum. It is also contemplated that the sprocket 80 could be made ofa composite including carbon fibers. A composition of the sprocket 80may be selected from a wide variety of substances. It is contemplatedthat the sprocket teeth 90, 100, 110 could be formed separately from thesprocket wheel 150 and subsequently rigidly fastened (via rivets, welds,bolts, etc.) to the sprocket wheel 150.

With reference to FIGS. 5 to 10, a first embodiment of the endless drivetrack 30 will be described. The endless drive track 30 has an endlessflexible belt 220 which has an inner surface 220 a and an outer surface220 b and edges 222. The endless drive track 30 defines a longitudinaldirection 5 and a lateral direction 6 for the drive track 30. In thedescription of the drive track below, the terms “longitudinal” and“lateral” are used with respect to the respective directions as definedby the drive track 30. The edges 222 are thus longitudinally extendingedges 222. When the drive track 30 is mounted on the snowmobile 10, thelongitudinal direction 5 defined by a given portion of the drive track30 can be different from the longitudinal direction 3 defined for thesnowmobile 10 by the tunnel 18. The lateral direction 6 defined by thedrive track 30 is the same as the lateral direction 4 defined by thetunnel 18 when the drive track 30 is mounted on the snowmobile 10.

The endless drive track 30 includes a plurality of external lugs 230that project outwardly from the outer side 220 b and a plurality ofinternal lugs 260 that project inwardly from the inner side 220 a. Theplurality of external lugs 230 provide the endless drive track 30 withtraction against snow as the endless drive track 30 propels thesnowmobile 10. As mentioned above, the internal lugs 260 are engaged bythe axial teeth 90, 110 so as to move the belt 220 around the suspensionassembly 32.

The endless drive track 30 is made of a strong, flexible material suchas rubber reinforced with fabric and metal. The endless belt 220, theexternal lugs 230 and the internal lugs 260 are integrally formed witheach other.

The endless belt 220 has a width (measured in the lateral direction 6between edges 222) of 40.64 cm (16 inches). It is contemplated that thewidth of the endless belt 220 could be more or less than 40.64 cm (16inches). For example, the width could be 33.02 cm (13 inches), 35.56 cm(14 inches), 35.56 cm (15 inches), 50.8 cm (20 inches) or 60 cm (24inches).

A length of the endless belt 220 (measured in the longitudinal direction5) is 147 inches (373.38 cm). It is contemplated that the length of theendless belt 220 could be more or less than 147 inches. The length ofthe belt could be any multiple of the lug pitches 238 and 266 discussedfurther below.

The plurality of internal lugs 260 includes inner track lugs 120, 130and outer track lugs 140. The inner track lugs 130 and the outer tracklugs 140 come in contact with the two sprockets 80 for providingtraction to the snowmobile 10. The inner track lugs 130 and the outertrack lugs 140 also come in contact with the slide rail 34 for ensuringthat the endless belt 220 stays in alignment. All of the internal lugs260 are identical to each other in the embodiment shown in FIGS. 5 to10. It is contemplated however that the lugs 260 could not all beidentical and could include two or more different kinds of internal lugs260.

The inner internal lugs 120 form two longitudinal rows 122, the innerinternal lugs 130 form two longitudinal rows 132, and the outer internallugs 140 form two longitudinal rows 142. The inner internal lugs 120 arealigned with the inner internal lugs 130 and the outer internal lugs 140in the longitudinal direction 5 so as to form lateral rows 264. It ishowever contemplated that some or all of the internal lugs 120 could beoffset from the corresponding lugs 130 and/or 140. Similarly some or allthe lugs 130 could be offset from the corresponding lugs 140.

The lateral rows 264 of internal lugs 120, 130, 140 are spaced at aninternal lug pitch 266 of approximately 7.62 cm (3 inches). The internallug pitch 266 is defined with respect to the longitudinal centers ofconsecutive lugs 260 of consecutive rows 264. It should be understoodthat the actual value of the lug pitch 266 in a given region of thedrive track 30 can vary from the stated value of the lug pitch 266 dueto manufacturing tolerances or due to the resilient deformation of themoving drive track 30.

It is contemplated that the internal lug pitch 266 could be more or lessthan 7.62 cm (3 inches). It is also contemplated that the inner lugpitch of the inner track lugs 120 could be different from the inner lugpitch of the inner track lugs 130 and/or the outer lug pitch of theouter lugs 140. It is also contemplated that the inner lug pitch of theinner track lugs 130 could be different from the outer lug pitch of theouter lugs 140. It is further contemplated that more than one internallug pitch 266 could be defined by the longitudinal spacing between twoconsecutive track lugs 120 and/or 130 and/or 140.

The configuration, including alignment and spacing, of the inner lugs130 with the outer lugs 140 is complementary to the configuration of theaxial teeth 90, 110. Thus, the internal lug pitch 266 can be equal tothe circumferential sprocket pitch 86 of the axial teeth 90, 110. Theinternal lug pitch 266 could also be a multiple or a factor of the pitch86.

As best seen in FIGS. 6A, 6B and 8, the internal lugs 260 extend inwardsfrom the surface 220 a to a height 262 (measured in a direction normalto the inner surface 220 a, i.e. perpendicular to the longitudinaldirection 5 and the lateral direction 6) which is about 1.27 cm (0.5inches). It is contemplated that the height 262 could be more or lessthan 1.27 cm (0.5 inches). The height 262 of the internal lugs 260 issmaller than the pitch 234 of the internal lugs. In the illustratedembodiments, all the internal lugs 260 have the same height 262. It ishowever contemplated that the height 262 of some of the internal lugs260 could be different from the height 262 of other internal lugs 260.

Each internal lug 260 has a longitudinal width 267 (FIGS. 6A, 6B and 7)measured in the longitudinal direction 5. Each internal lug has alateral width 268 measured in the lateral direction (FIG. 7).

A plurality of longitudinally spaced apertures (or windows) 240 aredefined in the endless belt 220. Each aperture 240 extends through thebelt 220 between the inner and outer surfaces 220 a and 220 b. Theapertures 240 are disposed in two longitudinal rows 242. It iscontemplated that the plurality of longitudinally spaced apertures 240could be disposed in a fashion other than in a longitudinal row. It isalso contemplated that the plurality of longitudinally spaced apertures240 could form only one row 242 or more than two rows 242.

The apertures 240 are engaged by the radial sprocket teeth 100 formoving the belt 220. It is contemplated that the plurality oflongitudinally spaced apertures 240 could be omitted for use withsprockets 80 from which radial teeth 100 are omitted. The configurationof the apertures 240, including spacing and alignment with inner lugs130 and the outer lugs 140 is complementary to the configuration of theradial teeth 100, including the spacing therebetween and alignment withaxial teeth 90, 110. The shape of each aperture 240 is generallyrectangular to engage the generally rectangular contour of the radialteeth 100. It is contemplated that the shape of the apertures 240 andradial teeth 100 could be different, such as circular or elliptical, butcomplementary to enable engagement between the teeth 100 and belt 220.

The endless drive track 30 also comprises a plurality of alignmentcleats 250 that are mounted onto the outer track lugs 140 and extend inbetween the apertures 240 as can be seen best in FIG. 9. Each cleat 250includes a base portion 250 a and a cleat portion 250 b. The baseportion 250 a has a generally C-shaped cross-section that wraps aroundthe inner track lugs 120, 130. The cleat portion 250 b projects inwardlyaway from the inner side 220 a of the belt 220. The alignment cleats 250are made of a strong, light, stamped sheet of metal such as steel. Aswould be appreciated by those skilled in the art, however, any othersuitable material (e.g., aluminum, etc.) may be used. Moreover, thecleats 250 need not be stamped from a metal sheet but may be cast ormolded into the appropriate configuration.

The plurality of external lugs 230 form a plurality of external luglateral rows 232. Each external lug lateral row 232 contains twoexternal lugs 230. The external lugs 230 of different lateral rows 232are aligned in the longitudinal direction to form two longitudinal rows231 (indicated in FIGS. 5 and 12A). A rib 224 (FIGS. 5 and 9) extendslaterally along the outer surface 220 b between the lateral edges 222.The rib 224, formed by a metal rod 225 (shown schematically in FIGS. 6Aand 6B) underneath the rubber surface 220 b of the belt 220, providesstructural support to the belt 220. Each lateral row 232 coincides witha rib 224 passing through the base of each lug 230 thereof. Therefore,in the illustrated embodiment, all of the rows 232 have ribs 224extending therealong. It is however contemplated that some of the ribs224 could not coincide with a row 232. For example, only alternatelateral rows 232 could coincide with a rib 224. It is also contemplatedthat the ribs 224 could also be omitted.

All of the external lugs 230 are identical to each other in theembodiment shown in FIGS. 5 to 10. Each external lug 230 is elongated inthe lateral direction and has a uniform lateral width 236 (FIG. 5)between longitudinally extending left and right surfaces. Thelongitudinal width 237 (FIGS. 6A and 6B) between laterally extendingsurfaces of each lug 230 decreases with distance away from the surface220 b. It is contemplated that the lugs 230 could not all be identicaland include two or more different kinds of external lugs 230 as shown inFIGS. 11A and 11B.

The external lugs 230 of each lateral row 232 are separated by alaterally separation 234 (FIG. 5). In the illustrated embodiment, thelateral separation 234 is generally equal to the lateral width 236. Itis contemplated that the lateral separation 234 between two lugs 230could be different from the lateral width 236 of each lug 230.

The longitudinally spacing between the external lug lateral rows 232 isan external lug pitch 238 of approximately 7.62 cm (3 inches) (best seenin FIGS. 6A and 6B). The external lug pitch 238 is defined with respectto the longitudinal centers of consecutive lugs 230 of consecutive rows232. The external lug pitch 238 can also be measured with respect to thecenters of consecutive rods 225. The external lug pitch 238 is equal tothe internal lug pitch 266. It is contemplated that the external lugpitch 238 could be smaller or greater than the internal lug pitch 266.It is contemplated that the external lug pitch 238 could be more or lessthan 7.62 cm (3 inches). It is also contemplated that more than oneexternal lug pitch 238 could exist between the external lug longitudinalrows 232. It should be understood that the actual value of the externallug pitch 238 in a given region of the drive track 30 can vary from thestated value of the external lug pitch 238 due to manufacturingtolerances or due to the resilient deformation of the moving drive track30.

Each external lug 230 has a height 239 (measured in a direction normalto the outer surface 220 b, i.e. perpendicular to the longitudinaldirection 5 and the lateral direction 6) of the external lugs 260. Theheight of the external lugs 230 of the drive track 30 shown in FIG. 6Ais 8.26 cm (3.25 inches). It is contemplated that the height 239 couldbe more or less than 8.26 cm (3.25 inches). For example, FIG. 6B shows adrive track 30 having internal lugs 230 with a height of 10.16 cm (4inches). The height 239 of the external lugs 230 is greater than theexternal lug pitch 238.

Increasing the lug height 239 provides increased traction which would beuseful for travel in powdered snow-covered surfaces. It is alsoimportant for the drive track 30 to have traction with the sprocket 80and thus to maintain sufficient contact between therebetween. In theconfiguration of the drive track 30 and sprocket 80 shown herein, atleast three consecutive sprocket teeth 90, 100, 110 are in contact withthe drive track 30 at all times which minimizes ratcheting caused by thesprocket 80 slipping with respect to the drive track 30.

Turning now to FIGS. 11A and 11B, a second embodiment of an endlessdrive track 30′ will be described. The endless drive track 30′ hasfeatures similar to the ones of the endless drive track 30. Thesefeatures will be referred to using the same reference numerals as theones of the endless drive track 30, and will not be described againherein in detail.

The endless drive track 30′ includes a plurality of external lugs 230 onan outer face 220 b of the endless belt 220. The plurality of externallugs 230 form lateral rows 232 that are longitudinally spaced by anexternal lug pitch 238 equal to 7.62 cm (3 inches). Each lateral row 232contains either one external lug 230 or two external lugs 230. Alternaterows 232 contain one external lug 230. Each lug 230 of the drive track30′ is an elongated structure similar to the lugs 230 of the drive track30. The rib 224 extends longitudinally along the outer surface 220 bbetween the lateral edges 222. Each row 232 coincides with a rib 224passing through the bases of the lugs 230 thereof.

More specifically, the external lugs 230 comprise two kinds of externallugs 230 a and 230 b. The lateral rows 232 comprise alternating rows 232a and 232 b.

The lugs 230 a are disposed in the center of rows 232 a of the lateralrows 232. The lugs 230 a are thus aligned in the longitudinal directionto form a single longitudinal row 231 a. A middle portion 274 of eachlug 230 a is angled forward (when the outer surface 220 b is on thebottom of the drive track 30) towards the lateral center of the lug 230a. The height 239 a of each lugs 230 a is greater than the external lugpitch 238 between consecutive rows 232 (i.e. between consecutive rows232 a and 232 b).

The lugs 230 b are disposed in rows 232 b of the lateral rows 232. Thetwo lugs 230 b are mirror images of each other and laterally spaced by adistance 234 b (FIG. 11B). The lugs 230 b of different lateral rows 232b are aligned in the longitudinal direction to form two longitudinalrows 231 b. The laterally extending front and rear surfaces of each lug230 b are discontinuous with a step 272 and a recesses 270 extendinginto the laterally extending surfaces of each external lug 232 b. Therecess 270 extends upwards from the surface 220 b but does not extend tothe top edge of the lug 230 b. The lugs 230 b have a height 239 b whichis smaller than the external lug pitch 238. The lateral width 236 a ofthe lugs 230 a is greater than the lateral width 232 b of the lugs 230b.

Turning now to FIGS. 12A and 12B, a third embodiment of an endless drivetrack 30″ will be described. The endless drive track 30″ has featuressimilar to the ones of the endless drive track 30. These features willbe referred to using the same reference numerals as the ones of theendless drive track 30, and will not be described again herein indetail.

The drive track 30″ has a plurality of external lugs 230 disposed inlateral rows 232 with a pitch 238 of approximately 7.62 cm (3 inches).Each lateral row has a left lug 230 disposed at the left end and a rightlug 230 disposed at the right end, that is a mirror image of the leftlug 230, so as to form two longitudinal rows 231 that are mirror imagesof one another. Each lug 230 extends inwards from its correspondinglongitudinally extending edge 222 of the drive track 30″. A recess 270extends into the laterally extending surfaces of each lug 230. Therecesses 270 are disposed slightly inward of the lateral center of thelug 230. The recesses 270 extend upwards from the base of the lug 230.

The belt 220″ of the drive track 30″ has longitudinal recesses 280extending through the belt 220 between the inner and outer surfaces 220a, and 220 b. The recesses 280 extend longitudinally through the entirelength of the belt 220 under the longitudinal row of lugs 231. Therecesses 280 of the belt 220 coincide with the recesses 270 of the lugs230.

As the drive track 30, 30′, or 30″ rotates about the rear suspensionassembly 32 propelling the snowmobile 10 on ground covered with snow andice, some of the snow and ice from the ground is projected upwards ontothe tunnel 18 and is used to cool the engine 24.

In the embodiment of the snowmobile 10 shown in FIGS. 3 and 4, a part ofthe tunnel 18 is formed by a heat exchanger assembly 400 for cooling theengine 24. The heat exchanger assembly 400 includes a front heatexchanger (not shown) connected to the front of the tunnel 18, and a topheat exchanger 408 connected to the top of the tunnel 18. Thus the gap18 c of the tunnel 18 is almost entirely covered with the heat exchangerassembly 400.

Liquid coolant is circulated through the engine 24 in order to cool theengine 24. The coolant, which gets heated by absorbing heat from theengine 24, is cooled by circulating through the heat exchanger assembly400. The coolant in the heat exchanger assembly 400 is cooled by acombination of air flowing along the surfaces of the heat exchangers andsnow being projected on to the heat exchanger surfaces by the drivetrack 30, 30′, or 30″. Fins formed along the rear surface of the frontheat exchanger and the bottom surface of the top heat exchanger 408increase the surface area exposed to the cold air, snow and ice for moreefficient cooling of the coolant flowing inside.

Another embodiment of a heat exchanger assembly 300 will now bedescribed with reference to FIGS. 13 to 15D.

With reference to FIGS. 13 and 14, the heat exchanger assembly 300includes a front heat exchanger 302, conduits 304, 306 and a top heatexchanger 308.

With reference to FIGS. 14 to 15B, the conduits 304, 306 are disposedadjacent the top 18 a of the tunnel 18 in the front portion thereof. Theleft conduit 304 extends longitudinally on the left side of thelongitudinal centerplane 13. The right conduit 306 extendslongitudinally on the right side of the longitudinal centerplane 13. Theconduits 304, 306 are formed by an extrusion process. It is contemplatedthat the conduits 304, 306 could be formed using a process other thanextrusion. With reference to FIG. 13, a pipe 344 connected to the frontend of the left conduit 304 extends vertically upwards through a plate354 that is disposed over the gap 18 c of the tunnel 18. Another pipe346 connected to the front end of the right conduit 306 extendsvertically upwards through the plate 354. The pipe 346 is disposedlongitudinally rearwardly of the pipe 344. The pipe 346 is connected tothe engine 24 via a hose 348 to receive heated coolant therefrom. Thepipe 344 is connected to an inlet 314 of the front heat exchanger 302 bya hose 347. A portion of the conduits 304, 306 and/or the pipes 344, 346is fixed to the plate 354. The plate 354 thus supports the conduits 304,306 and the pipes 344, 346, helping prevent them from bending downwardtoward the drive track 30, 30′, or 30″. The plate 354 is riveted to theleft and right tunnel side walls 18 b. It is contemplated that the plate354 could be fixed to the side walls 18 b by other types of fasteners.

With reference to FIGS. 13, 14 and 15B to 15D, the top heat exchanger308 is disposed on the rear portion of the top wall 18 a over the gap 18c of the tunnel 18. The top heat exchanger 308 thus defines partly a topof the tunnel 18. The top heat exchanger 308 is riveted to the left andright tunnel side walls 18 b. It is contemplated that the top heatexchanger 308 could be fixed to the side walls 18 b by other types offasteners.

The top heat exchanger 308 has a body 320 with a right passage 328 and aleft passage 326. As can be seen in FIG. 15C, the width W of eachpassage 326 and 328 is greater than its maximum height H. The heatexchanger 308 is formed by an extrusion process. As can be seen in FIG.14, the rear end of the left conduit 304 is welded to an outlet 322formed at the front end of the left passage 326. The left conduit 304 isthus fluidly connected to the top heat exchanger 308. The rear end ofthe right conduit 306 is similarly welded to an inlet 324 formed at thefront end of the right passage 328 to fluidly connect the top heatexchanger 308 with the right conduit 306. Fins 332 are formed on thebottom of the body 320. A connector 330, also formed by extrusion, isconnected to the back of the two passages 326, 328 to fluidly connectthe passage 326 to the passage 328.

As can be seen in FIG. 15D, the top heat exchanger 308 therefore extendsfrom the rear end of the tunnel 18 to a position longitudinally forwardof the bracket 352 which attaches the upper idler wheel 44 to the tunnel18, and thereby suspends the drive track 30, 30′, or 30″ to the tunnel18. This area is considered to provide the best snow projection onto theheat exchanger 308 due to the directional change of the drive track 30.Passages 326 and 328 of heat exchanger 308 have a width W that issubstantially greater than the diameter of conduits 304 and 306. Theprimary task of the conduits 304 and 306 is to transfer fluid betweenheat exchangers 302 and 308 thus their shape and material is notdetermined based on their heat exchanging characteristics as is the casewith heat exchangers 302 and 308. Conduits 304 and 306 could beconstructed from a rigid metal or a flexible material and their heatexchanging characteristics is lower than of the heat exchanger 308 for agiven longitudinal distance.

With reference to FIGS. 13 to 15A, the front heat exchanger 302 has abody 310 defining an internal volume, an outlet pipe 312 and an inletpipe 314. The pipes 312, 314 are welded to the body 310. The inlet pipe314 is disposed above the outlet pipe 312. As mentioned above, the inletpipe 314 is connected to the left conduit 304 via the hose 347. Theoutlet pipe 312 is connected to a hose 350 (FIG. 13) which is connectedto the engine 24 to return cooled coolant thereto. Fins 316 are formedon the back of the body 310 as can be seen in FIG. 15A. The front heatexchanger 302 forms in part the lower portion of the front of the tunnel18.

During operation of the snowmobile 10, heated coolant from the engine 24flows via the hose 348 and the inlet pipe 346 to the right conduit 306.From the right conduit 306, the coolant flows via the inlet 324 into theright passage 328 of the top heat exchanger 308, then into the connector330 and then to the left passage 326. The coolant then flows out of thetop heat exchanger 308 via the outlet 322 of the left passage 326 intothe left conduit 304 and then via its outlet pipe 344 and the hose 347into the inlet 314 of the front heat exchanger 302. The coolant flowsthrough the interior volume of the front heat exchanger 302 and outthereof via the outlet 312. The cooled coolant is then returned to theengine 24 via the hose 350.

A greater amount of snow is projected onto the front of the tunnel 18and the rear portion of the top of the tunnel 18 than in the forwardportion of the top of the tunnel 18. Therefore, using conduits 304, 306to conduct coolant between the front of the tunnel 18 and the rearportion of the top of the tunnel 18 which receive more projected snowallows one to reduce the overall weight of the snowmobile 10 withoutsignificantly sacrificing cooling efficiency of the heat exchangerassembly 300. The heat exchanger assembly 300 in a snowmobile 10 havingthe drive track 30, 30′, or 30″ described above allows for compensationof the increased weight of the snowmobile 10 due to the heavier externallugs 230 described above.

The heat exchanger assembly 300 is also advantageous for weightcompensation in a snowmobile 10 having a longer and thus a heavier drivetrack 30, 30′, or 30″. For example, in a snowmobile 10 having a longerdrive track 30, 30′, or 30″ with a circumference (measured in thelongitudinal direction) of 441.96 cm (174 inches) or 414.02 cm (163inches) rather than a circumference of 373.38 cm (147 inches), the heatexchanger assembly 300 described above can provide adequate enginecooling while also reducing the overall weight of the snowmobile 10 tocompensate for the additional weight of the drive track 30, 30′ or 30″.

Modifications and improvements to the above-described embodiments of thepresent technology may become apparent to those skilled in the art. Theforegoing description is intended to be exemplary rather than limiting.The scope of the present technology is therefore intended to be limitedsolely by the scope of the appended claims.

What is claimed is:
 1. A drive track for a tracked vehicle, the drivetrack comprising: an endless belt having an inner surface and an outersurface, the belt defining a longitudinal direction and a lateraldirection; and a plurality of external lugs projecting outwards from theouter surface of the belt, each of the plurality of external lugs havinga height in a direction normal to the outer surface, the plurality ofexternal lugs forming a plurality of lateral rows, a longitudinalspacing between consecutive lateral rows of the plurality of lateralrows being an external lug pitch; and the height of at least one of theplurality of external lugs being greater than the external lug pitch. 2.The drive track of claim 1, wherein the height of all of the externallugs of at least one of the lateral rows is greater than the externallug pitch.
 3. The drive track of claim 1, wherein the height of all ofthe plurality of external lugs is greater than the external lug pitch.4. The drive track of claim 1, wherein alternating lateral rows haveequal numbers of external lugs.
 5. The drive track of claim 1, whereinthe external lug pitch is 7.62 cm (3 inches).
 6. The drive track ofclaim 1, further comprising a plurality of internal lugs projectinginwards from the inner surface of the belt, the plurality of internallugs forming at least one longitudinal row, a longitudinal spacingbetween consecutive internal lugs of the at least one longitudinal rowbeing an internal lug pitch.
 7. A snowmobile comprising: a frame; asuspension assembly connected to the frame; an engine connected to theframe; a drive axle operatively connected to the engine; at least onedrive sprocket mounted on the drive axle and being rotatable therewith,each of the at least one drive sprocket comprising: a wheel mounted onthe drive axle; and a plurality of teeth being distributed on aperiphery of the wheel, a circumferential spacing between consecutiveteeth of the plurality of teeth being a sprocket pitch; and a drivetrack connected to the frame by the suspension assembly, the at leastone drive sprocket driving the drive track about the suspension assemblyto propel the snowmobile, the drive track comprising: an endless belthaving an inner surface and an outer surface, the belt defining alongitudinal direction and a lateral direction; and a plurality ofexternal lugs projecting outwards from the outer surface of the belt,each of the plurality of external lugs having a height in a directionnormal to the outer surface, the plurality of external lugs forming aplurality of lateral rows, a longitudinal spacing between consecutivelateral rows of the plurality of lateral rows being an external lugpitch, the height of at least one of the plurality of external lugsbeing greater than the external lug pitch.
 8. The snowmobile of claim 7further comprising: a plurality of internal lugs projecting inwards fromthe inner surface of the belt, each of the plurality of teeth beingadapted to selectively engage at least one of the plurality of internallugs, the plurality of internal lugs forming at least one longitudinalrow, a longitudinal spacing between consecutive internal lugs of the atleast one longitudinal row being an internal lug pitch, the internal lugpitch being complementary to the sprocket pitch of the at least onedrive sprocket such that two consecutive sprocket teeth of the pluralityof sprocket teeth of the at least one drive sprocket contact one of theinternal lugs.
 9. The snowmobile of claim 8, wherein the wheel of thedrive sprocket has a diameter such that the plurality of teeth engagesat least three of the plurality of internal lugs.
 10. The snowmobile ofclaim 7, wherein the plurality of teeth comprises: a plurality of axialteeth being distributed on a periphery of an axial surface of the wheeland extending therefrom in an axial direction of the drive axle.
 11. Thesnowmobile of claim 10, wherein the plurality of axial teeth is at leastseven axial teeth.
 12. The snowmobile of claim 11, wherein the pluralityof axial teeth is seven axial teeth.
 13. The snowmobile of claim 7,wherein: the plurality of teeth comprises a plurality of radial teethdistributed on a perimetrical surface of the wheel and extendingradially therefrom; and the drive track comprises a plurality of beltapertures extending through the belt from the inner surface to the outersurface, the belt apertures forming at least one longitudinal row ofbelt apertures, the longitudinal spacing between consecutive beltapertures of the at least one longitudinal row of belt apertures being abelt aperture pitch; and the belt aperture pitch corresponding to thesprocket pitch of the radial teeth such that each of the plurality ofradial teeth selectively engages a corresponding belt aperture when asurface of the wheel adjacent to the corresponding radial tooth is incontact with the inner surface adjacent the corresponding belt aperture.14. The snowmobile of claim 7, wherein the external lug pitch is 7.62 cm(3 inches).
 15. The snowmobile of claim 7, further comprising a brakedisk mounted on the drive axle, the brake disk being coaxial androtatable with the drive axle, a diameter of the brake disk beinggreater than a diameter of the wheel of the at least one drive sprocket.16. The snowmobile of claim 15, wherein the diameter of the brake diskis greater than a diameter of a cylinder circumscribing the entirety ofthe at least one drive sprocket.
 17. The snowmobile of claim 7, wherein:the frame comprises a tunnel; the tunnel comprises a left side walldefining a left opening and a right side wall defining a right opening;the drive axle extends through the left opening and the right opening;and the drive axle and the at least one drive sprocket mounted thereonare rotatable about a drive sprocket axis, the snowmobile furthercomprising: a left footrest extending laterally outwardly from the leftside wall, a portion of the left footrest being disposed longitudinallyforwardly of the drive sprocket axis, a projection of the left footreston the left side wall being disposed in part within a perimeter of theleft opening; and a right footrest extending laterally outwardly fromthe right side wall, a portion of the right footrest being disposedlongitudinally forwardly of the drive sprocket axis, a projection of theright footrest on the right side wall being disposed in part within aperimeter of the right opening.
 18. The snowmobile of claim 7, wherein:the suspension assembly is a rear suspension assembly, the rearsuspension assembly comprising an upper idler wheel rotatable about anupper idler wheel rotation axis; the drive axle and the at least onedrive sprocket mounted thereon are rotatable about a drive sprocketaxis; and the snowmobile further comprises: a left ski assembly; a rightski assembly; a left front suspension assembly connecting the left skiassembly to the frame; and a right front suspension assembly connectingthe right ski assembly to the frame, each of the left and right frontsuspension assemblies comprising an arm having a front member and a rearmember, respective inner ends of each of the front and rear membersbeing pivotally connected to the frame about an arm pivot axis, wherein,for each of the left and right suspension assemblies: an intersection ofthe arm pivot axis with a plane containing the upper idler wheelrotation axis and the drive sprocket axis is disposed longitudinallybetween the inner ends of the front member and the rear member.
 19. Thesnowmobile of claim 18, wherein: the arm is a lower arm; and each of theleft and right front suspension assemblies further comprises an upperarm.
 20. A drive sprocket and drive track assembly of a tracked vehicle,the assembly comprising: a drive track comprising: an endless belthaving an inner surface and an outer surface, the belt defining alongitudinal direction and a lateral direction; and a plurality ofexternal lugs projecting outwards from the outer surface of the belt,each of the plurality of external lugs having a height in a directionnormal to the outer surface, the plurality of external lugs forming aplurality of lateral rows, a longitudinal spacing between consecutivelateral rows of the plurality of lateral rows being an external lugpitch, the height of at least one of the plurality of external lugsbeing greater than the external lug pitch; and a plurality of internallugs projecting inwards from the inner surface of the belt, theplurality of internal lugs forming at least one longitudinal row, alongitudinal spacing between consecutive internal lugs of the at leastone longitudinal row being an internal lug pitch; and at least one drivesprocket, each of the at least one drive sprocket comprising: a wheelmounted on the drive axle; and a plurality of teeth being distributed ona periphery of the wheel, a circumferential spacing between consecutiveteeth of the plurality of teeth being a sprocket pitch, each of theplurality of teeth being adapted to engage at least one of the pluralityof internal lugs, the internal lug pitch being complementary to thedrive sprocket pitch of the at least one drive sprocket such that twoconsecutive teeth of the plurality of teeth of the at least one drivesprocket contact one of the internal lugs.
 21. The assembly of claim 20,wherein the sprocket has a diameter such that the plurality of teethengages at least three of the plurality of internal lugs.